In the solution ring opening polymerization of cycloolefins, the product discharged from the reactor is a honey-like cement that consists principally of a nonpolar carrier solvent in which the polymer is dissolved. The polymer content is normally on the order of about 15% by weight. The polymer can be any of the family of polymers that are made by homopolymerization or copolymerization of one or more of cycloolefins that contain the norbornene group. Polymerization can be conducted either batchwise or continuously.
After the honey-like cement is prepared, it is necessary to separate the polymer from its carrier solvent. In the past, steam stripping has been used exclusively in plant operations to extract the polymer from the carrier solvent. In steam stripping, the cement is injected into a jet of steam that is directed into a vessel containing hot water. As contact is made between the cement and the jet of steam, the carrier solvent is flashed off as vapor, depositing the polymer in particle form in the hot water.
Due to many disadvantages that accompany steam stripping of polycycloolefin cements, it is no longer used.
More recently, an alternate approach was discovered for isolating polymers of cycloolefins from the carrier solvent. Pursuant to this approach, the cement is mixed in a high shear mixer with a nonsolvent in the volume ratio of about 3 to 1 nonsolvent to cement whereby the polymer precipitates out. A nonsolvent is a liquid that is miscible with the nonpolar solvent that is used in the polymerization reaction but is a nonsolvent for the polymer. Examples of suitable nonsolvents include ethanol, n-propanol, isopropanol, and the like. Although on some occasions this recovery procedure produced granular, easy-to-dry product having bulk density of about 0.144 g/cc or 9 lb/ft.sup.3, these results could not be reliably reproduced. What was obtained normally was a clump-like product of fine, irregular fluffy microfibers that packed cottonlike when filtered and was difficult to dry, the dry product having bulk density below 0.08 g/cc or 5 lb/ft.sup.3.
When polymer cement is precipitated or coagulated in a nonsolvent medium, the high polymers appear to precipitate from and the oligomers, catalyst residues, and the like, remain solubilized in the mixed nonsolvent-solvent medium. Since a substantial portion of the impurities are soluble in the nonsolvent, this recovery process succeeded in removing the bulk of the impurities from the polymer. However, this approach was not entirely successful since large volumes of contaminated liquid was produced composed primarily of nonsolvent, cyclic nonpolar reaction solvent, and impurities that included residual shortstop for the polymerization reaction, adducts of the shortstop with catalyst residues, residual catalyst components, oligomers, etc. Solvent recovery of the large volume of nonsolvent-solvent liquid is difficult and expensive, and especially complicated using water-free nonsolvents which azeotrope with water and the solvent.
More specifically, in reference to the use of a nonsolvent in polymer extraction, at bottom of col. 4 of the Minchak U.S. Pat. No. 4,069,376 it is disclosed that a polymer of one or more cycloolefins can be isolated by precipitation using a nonsolvent selected from lower alcohols such as methanol, ethanol, isopropanol, and the like. This is a known method wherein polymer cement and a nonsolvent are mixed in a high-shear intensive mixer whereby a slurry is formed. The slurry is then conveyed to a slurry tank where it is further agitated at ambient temperature, and from the tank the slurry is taken to a centrifuge or a filter where the polymer is separated and taken to a drying operation, whereas the filtrate is pumped to a recovery operation where the cyclic nonpolar solvent is separated from the nonsolvent and recovered. The filtrate is composed essentially of the cyclic nonpolar solvent and the nonsolvent hydrocarbon.